Collection Information

This item is part of the Geosciences Theses collection. It was digitized from a physical copy provided by the Antevs Library, Department of Geosciences, University of Arizona. For more information about items in this collection, please email the Antevs Library, antevs@geo.arizona.edu.

Abstract

Assemblages of Paleozoic age and less significant Triassic and possibly Cretaceous-Tertiary volcanic rocks constitute the Sierra El Aliso, 186 km east-southeast of Hermosillo, Sonora. The Paleozoic section consists of approximately 2000 m of allochthonous Ordovician to Permian pelagic and hemipelagic deposits that accumulated in continental slope, continental rise and ocean floor (?) environments. The lower Paleozoic is characterized by graptolitic black shale and radiolarian chert, quartzite, argillite and local limestone. The upper Paleozoic is predominantly turbidite carbonates rich in benthonic foraminifera, and conodont faunas, subordinate bedded chert, siltstone, sandstone and chert-clast conglomerate. After Early Permian time, but prior to the deposition of the Late Triassic Barranca Group the Paleozoic section was imbricated along south-southeast vergent thrust faults. The Triassic rocks unconformably overlie the Paleo-zoic strata and all thrust faults. The Triassic and older rocks are overlain by the Cretaceous-Tertiary volcanics.

Related items

Swetnam, Thomas W.; Laboratory of Tree-Ring Research, University of Arizona (Laboratory of Tree-Ring Research, University of Arizona (Tucson, AZ), 1985-10-31)

Regional outbreaks of western spruce budworms (Choristoneura occidentalis Freeman) have recurred at least three times in northern New Mexico since the early 1920's when the U. S. Forest Service first began systematic forest-pest surveys and documentation (Lessard 1975, U. S. Forest Service documents). The current outbreak was first noticed in a small area on the Taos Indian Reservation in 1974, and since then the defoliated areas have increased in New Mexico and Arizona to more than 370,000 acres of Federal, Indian, State and private lands (Linnane 1984). Losses in timber values can generally be ascribed to radial growth loss, height growth loss, topkilling, reduced regeneration, and mortality (Carlson et al. 1983, Fellin et al. 1983). A damage assessment project was initiated in 1978 and was aimed at obtaining measurements of some of these losses in budworm infested stands on the Carson National Forest, New Mexico (Holland and Lessard 1979). A large data base has subsequently been developed, including yearly measurements on topkilling, mortality, defoliation, and insect population changes (Stein 1980, 1981, Stein and McDonnell 1982, Rogers 1984). A growth assessment study was undertaken in 1982 to determine the feasibility of using dendrochronological methods to identify the timing of past outbreaks and to quantify radial growth losses associated with budworm defoliation (Swetnam 1984). Results of this work showed that three major outbreaks during the twentieth century were clearly visible in the tree-ring samples obtained from currently infested trees. The radial growth of host trees was corrected for age, climate and other non-budworm environmental effects, and then growth losses were computed as a percentage of expected growth (Swetnam 1984). Additional collections were obtained in 1984 in order to expand the scope of the radial growth study. The objectives included 1) assessment of a larger number of tree -ring samples, 2) comparison of radial growth losses between the two primary host species - Douglas-fir (Pseudotsuga menziesii) and white fir (Abies concolor), 3) comparison of radial growth losses between age classes, and 4) analysis of the relationship between yearly measurements of defoliation, insect populations and radial growth. This report summarizes the findings of the above analyses. Increment core samples from the 1982 collections are included here, therefore this report supersedes the earlier report (Swetnam 1984). Information is also presented on observations derived from the dated tree-ring series on the timing of occurrence of known and inferred spruce budworm outbreaks for the past 284 years (1700- 1983). This is the longest record of spruce budworm occurrence yet developed for western North America.

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